Conventionally, there has been known a resistance film type touch panel as one of input means. In the resistance film type touch panel, two resistance films each having electrodes on both ends are opposed to each other via dot spacers. By the pressure of touch, the resistance film of a touch position contacts another resistance film. Thereby, the touch position is detected. Moreover, there has been known a method for detecting an abnormality of the resistance films beforehand by calculating a convergence electric potential (see Japanese Laid-open Patent Publication No. 11-24843).